Step |
Hyp |
Ref |
Expression |
1 |
|
vex |
|- x e. _V |
2 |
|
vex |
|- y e. _V |
3 |
1 2
|
op2ndd |
|- ( A = <. x , y >. -> ( 2nd ` A ) = y ) |
4 |
3
|
eqcomd |
|- ( A = <. x , y >. -> y = ( 2nd ` A ) ) |
5 |
|
sbceq1a |
|- ( y = ( 2nd ` A ) -> ( ph <-> [. ( 2nd ` A ) / y ]. ph ) ) |
6 |
4 5
|
syl |
|- ( A = <. x , y >. -> ( ph <-> [. ( 2nd ` A ) / y ]. ph ) ) |
7 |
1 2
|
op1std |
|- ( A = <. x , y >. -> ( 1st ` A ) = x ) |
8 |
7
|
eqcomd |
|- ( A = <. x , y >. -> x = ( 1st ` A ) ) |
9 |
|
sbceq1a |
|- ( x = ( 1st ` A ) -> ( [. ( 2nd ` A ) / y ]. ph <-> [. ( 1st ` A ) / x ]. [. ( 2nd ` A ) / y ]. ph ) ) |
10 |
8 9
|
syl |
|- ( A = <. x , y >. -> ( [. ( 2nd ` A ) / y ]. ph <-> [. ( 1st ` A ) / x ]. [. ( 2nd ` A ) / y ]. ph ) ) |
11 |
6 10
|
bitr2d |
|- ( A = <. x , y >. -> ( [. ( 1st ` A ) / x ]. [. ( 2nd ` A ) / y ]. ph <-> ph ) ) |